1. Field of Invention
The present invention relates to a light source using light-emitting diode (LED). More particularly, the present invention relates to a light source, which could have a color change approach to warm color when dimming the light.
2. Description of Related Art
LED is one of the light sources in various applications. Based on the properties of the LED, different LEDs could emit different colors, such as red, green, blue, or amber. For a light source as a lamp, it may need several LEDs to form a lamp. The popular lamp of LED is producing white light to replace the rather conventional filament incandescent lamp. Generally, the light emitted by the LED is relating to the color temperature, which is further relating to the operation voltage being applied. In order to have adjustable color temperature for the lamp, several conventional lamps including multiple LEDs under control have been proposed.
The disclosure of a patent of I226791 in Taiwan has disclosed a lamp, which uses three LEDs of red, green, and blue. Three LEDs are separately controlled with the operation voltage. The RGB lights produced by the RGB LEDs are mixed into a desired color.
Further in the disclosure of a patent of 532699 in Taiwan, a lamp is also designed with three LEDs. The three LEDs form as a unit and are covered by an envelope as a light bulb. Each LED is separately controlled by a different voltage to change the light brightness and color.
Further in the disclosure of a patent of M332777 in Taiwan, a lamp is designed with two types of LEDs, which are arranged in a 2D array at a plane. The first light emitting diode emits a light beam with a first color temperature and the second light emitting diode emits a light beam with a second color temperature. A control unit controls a variable resistance to modulate the current passing through the second light emitting diode. Thus, the color temperature of the lamp could be changed.
In the conventional design for the lamp, each different type of LED is separately controlled, so as to produce the mixed light in adjustable color. However, the dimming effect of the LED lamp is not taken into consideration.